Let's say Google would like candidates with PQ>130 with 95% confidence. Google has an error with std. div. of 15 points in measurement of PQ in jobs interviews. Google then needs to set the hiring bar at 160 PQ in order to get those candidates. This:
- screens most qualified candidates out; but
- most candidates who do screen in are qualified
Statistics would suggest this leaves you with 95% qualified candidates. A more precise Bayesian analysis will show you don't end up with 95% qualified employees, but the basic idea works -- it's still a majority. You set an impossibly high bar, so that candidates hired need to be qualified AND lucky. You discount unlucky candidates, but you don't hire (many) unqualified ones.
The problem, of course, is that all Googlers are convinced they all have a PQ>160, and are superior to everyone else. That's where you get the obnoxious Google incompetent arrogance.